Patrick Cordier (Villeneuve d'Ascq / FR; Paris / FR), Ihtasham ul Haq (Antwerp / BE), Andrey Orekhov (Antwerp / BE), Dominique Schryvers (Antwerp / BE), Hosni Idrissi (Antwerp / BE; Louvain-la-Neuve / BE)
Abstract text (incl. figure legends and references)
(Mg, Fe)2SiO4 olivine is the most volumetric abundant mineral phase in the upper mantle down to 410 km depth and also the one which deforms the most and controls the rheology of the upper mantle. Deformation mechanisms in olivine have attracted considerable attention since several decades. One of the problems with this orthorhombic mineral is that there are not enough slip systems to produce a general deformation. The observation of a non-linear deformation regime depending on the grain size has led to the suggestion of the possibility of slip at the grain boundary [1], which has only recently been demonstrated microstructurally [2]. In this paper we show that under high stresses, this grain boundary sliding can be due to the amorphization of the grain boundary and to the flow of this amorphous intergranular phase. We show how nanomechanical testing in situ in the TEM allows to characterize this individual mechanism as well as the rheology of this amorphous olivine. We finally propose that this mechanism of stress-induced amorphization is an important deformation mechanism in its own right under conditions of high stress [3].
[1] Hirth, G., & Kohlstedt, D. (1995) Experimental constraints on the dynamics of the partially molten upper mantle: 2. Deformation in the dislocation creep regime, Journal of Geophysical Research, 100, 15,441–15,449,
[2] Bollinger, C., Marquardt, K. & Ferreira, F. (2019) Intragranular plasticity vs. grain boundary sliding (GBS) in forsterite: microstructural evidence at high pressures (3.5–5.0 GPa). American Mineralogist 104, 220–231.
[3] Idrissi, H., Carrez, P., & Cordier, P. (2022) On amorphization as a deformation mechanism under high stresses. Current Opinion in Solid State & Materials Science. 26(1), 100976